Methods are known which control the composition of the mixture to a minimal consumption in the part-load range of an internal combustion engine. In the case of an optimizer or extreme-value control, it has already been suggested to oscillate or dither the quantity of air supplied to an internal combustion engine by means of a test signal. Because of the relatively long stretch between the bypass, the throttle flap and the individual cylinders, running times occur which limit the oscillating or wobble frequency and cause a relatively slow control behavior. Furthermore, an expensive positioning member, for example an air flap in an air bypass, is required.
To avoid these disadvantages, U.S. Pat. No. 4,478,186 discloses that for an extreme-value control to a minimum specific fuel consumption, the metered fuel quantity can be varied to define a test signal and to determine the operating point of the minimal fuel consumption of the engine versus maximum efficiency. In this connection, the maximum efficiency is determined by division starting with the quantities of torque of the internal combustion engine and fuel-metering signal. However, for this method too, a costly torque sensor as well as a computer unit for performing division are necessary.